DESCRIPTION (from applicant's abstract) The experiments proposed in this grant request are designed to examine the role of the cerebellum in the learning of two different cerebellar-dependent adaptive reaching movements, one to compensate for image displacing prisms and the other to compensate for the application of an elastic load capable of displacing the limb from its intended trajectory. The experiments assess the general hypothesis that the cerebellum's role in the learning of motor tasks is highly task-dependent. In the first group of experiments, the contribution of the cerebellum to prism adaptation will be explored in human subjects and in cats trained to reach for a manipulandum while wearing image displacing prisms. Our preliminary data indicate that this compensatory process is dependent on the cerebellum, but in a different manner than currently believed. In a second group of studies, human subjects and cats will be required to adapt to the application of an elastic load applied during a reaching movement. Preliminary studies indicate that this adaptation employs a response to the perturbation that is highly dependent upon on-line processing by the cerebellum. The experiments will determine the capacity of cerebellar patients and cats with inactivated ipsilateral interposed and dentate nuclei to acquire and retain these two types of adaptive behaviors. The cerebellar-dependent features of the adaptation acquired normally will be contrasted with those governing adaptation when the cerebellum is dysfunctional. The cat paradigms will be used to asses the neuronal interactions occurring in the cerebellum underlying the acquisition as well as the execution of these two types of adaptive behaviors. Multiple single unit recording in functionally related regions of the cerebellar cortex and nuclei will elucidate the neuronal interactions within a specific sagittal zone during both the acquisition and performance of these adaptive behaviors, emphasizing those interactions related to the cerebellar-dependent features of the learning process. The findings will reveal important principles related to the learning of motor behaviors, the basis for certain functional abnormalities in cerebellar patients, and general mechanisms which may be invoked during recovery of motor function following ablative pathology in the central nervous system.